I often find myself wanting to use standard data structures in TeX. For example, lists or maps. Each time this need comes up, I reinvent the wheel. For some reason, I find myself using stacks fairly frequently.
Is there a standard package (either plain TeX or LaTeX) that offers a convenient interface to data structures? They would be most useful if the structures could be combined so that you could have lists of maps, for example.
One of the ideas of expl3 is to provide a number of standard programming tools, and data structures are included in this. Currently, the structured data types available are sequences, stacks and property lists. Sequences and stacks have the same underlying structure: they are different ways of looking at the same thing. So we might have
\seq_new:N \l_my_seq
\seq_put_right:Nn \l_my_seq { Some-tokens } % Sequence-like access
\seq_push:Nn \l_my_seq { More-tokens } % Stack-like access, puts to left
Property lists are a key-value type data type
\prop_new:N \l_my_prop
\prop_put:Nnn \l_my_prop { key-name } { value }
Property lists are 'unordered', whereas sequences/stacks are ordered. In both cases there are functions available to map to each item in the stored data, for example \seq_map_function:NN.
New data types can be added to expl3 as needed: this depends on the requirements of the LaTeX3 Project but also of others. (Note of course that I'm on the LaTeX3 Project!)
An alternative set of packages providing some similar ideas to expl3 including a number of data-related structures is the combination of etoolbox and etextools. These two packages provide functions for mapping to lists and so on.
You might also look at the datatool package, which can be used to construct tables in LaTeX and access the data in a database-like fashion.
One other note. LuaTeX provides access to the native Lua data storage methods, which if you are doing a LuaTeX-only project would of course be the first place to look.
expl3, the naming has been off-putting. I take it it makes _ have catcode 11, same with :? Or I guess it could \def\seq_#1:{...}. At any rate, I'll take a look, thanks.
\ExplSyntaxOn...\ExplSyntaxOff colon and underscore have catcode 11.
Commented
Aug 29, 2010 at 10:17
@ as a letter, really, and fits more with what a lot of other languages do. (Plus avoids the business where @ is used in a more-or-less random way in names.)
\prop_put:Nnn and ask what this does. If she can answer it without asking back, the language (API) is good. If she can't, then rethink the language. Source code must be readable without having to translate everything in your head. Why? The more complex the translation process is, the more expensive is the code to maintain. And the less likely it is that someone actually uses that language. -- So my advise is to drop as much of the input language as you can and switch something more sensible, such as Lua.:)
I recently discovered the package arrayjobx (nee arrayjob) which has transformed my TeX usage. Linked lists and indexed references are very simple to do. Arrays combined with fp have allowed me to manage numerical data in TeX for display. Reading the code for arrayjobx was also very enlightening.
\documentclass{minimal}
\usepackage{arrayjobx}
\makeatletter
\usepackage{trimspaces}
\def\trimspace#1{\trim@spaces@in{#1}}
\makeatother
\begin{document}
\newarray\MyData
\readarray{MyData}{%
Years & 1996 & 1997 & 1998 & 1999 & 2000 &%
Revenues & 1034 & 1226 & 1445 & 1503 & 1992 &%
Costs & 668 & 706 & 813 & 946 & 1010 }
\dataheight=6
\def\returnHeading(#1){\checkMyData(#1,1)\trimspace\cachedata \cachedata}
\def\returnYear(#1){\checkMyData(1,#1)\trimspace\cachedata \cachedata}
\def\returnData(#1){\expandafter\checkMyData(#1)\trimspace\cachedata \cachedata}
\def\mycolumn{3}
\def\myrow{2}
Our expected \returnHeading(\myrow) in \returnYear(\mycolumn) were
\$\returnData(\myrow,\mycolumn).
\end{document}
On the other hand, I am not familiar with the packages mentioned in other answers. Maybe they render arrayjob obsolete.
Did no one mention the bridges to Lua in Luatex? Well, Patrick did, oblliquely.
\directlua command. Using this level is a bit fiddly.\startluacode ... \endluacode allows Lua to be naturally embedded in Context documents. This is important, because Context uses Lua to manage the whole compilation process.\LuaLaTeX macro, and similarly nice environments for embedding code. There's not much in Texlive 2009, and I've not made the jump to 2010 yet, but the document about supporting Luatex's hook in Latex, which Patrick pointed out to me, looks appetising.Lua has a nice, efficient, minimalist approach to datastructures, based on its notion of tables, that fuses lists and associative arrays, and is used together with its novel approach to lightweight closures as its basis for a prototype-based object system.
It's good, take a look.
I remember seeing some time ago in this site a link to lambda-lists aka lists in TeX's mouth by Alan Jeffrey. I haven't yet tried it out, though, but it sure seemed nice and functional.
